1. Field of the Invention
The present invention relates to a support for a lithographic printing plate, a method of preparing the support, and a presensitized plate. More particularly, the present invention relates to a support for a lithographic printing plate achieving both high scum resistance and long press life when processed into a lithographic printing plate, a method of preparing the support, and a presensitized plate using the support for a lithographic printing plate.
2. Description of the Related Art
It has been known that a hydrophilic treatment represented by a silicate treatment is performed on the surface of a lithographic printing plate after an anodizing treatment was performed thereon in order to enhance the development property of a presensitized plate. If a hydrophilic treatment is performed on the surface of a support for a lithographic printing plate, scum resistance is improved since ink which is hydrophobic is hardly adhered to non-image areas of a lithographic printing plate at the time of printing.
However, if a hydrophilic treatment is performed on the surface of a support for a lithographic printing plate, there is a case that an adhesion between an image recording layer which is hydrophobic and a support deteriorates in a presensitized plate, and press life deteriorates when processed into a lithographic printing plate.
Accordingly, a presensitized plate excellent in both scum resistance and press life when processed into a lithographic printing plate and a support for a lithographic printing plate for use in the presensitized plate are expected.
As a countermeasure thereto, a method for improving press life is proposed by further performing a treatment on the surface of a support for a lithographic printing plate with an aqueous solution containing heavy metals such as cobalt and zirconium after a hydrophilic treatment is performed thereon (JP 7-314937 A (the term “JP XX-XXXXXX A” as used herein means an “unexamined published Japanese patent application”) or the like). With the above method, although press life is improved, scum resistance deteriorates.
There is proposed a method of preparing a lithographic printing plate which comprises a graining treatment, an anodizing treatment, a hydrophilic treatment, application of a radiation-sensitive coating, exposure to light and development in an alkali aqueous solution, wherein the lithographic printing plate is obtained by treating with a salt solution containing a divalent or multivalent cation at a concentration of 0.02 mol/L or more after the hydrophilic treatment is performed (see JP 5-221178 A). However, this method may often impair scum resistance although deterioration of oxides (dissolution of an anodized layer) is prevented. In addition, the use of a salt solution at a high concentration increases the costs for disposal of the salt solution.
In the meanwhile, scum is likely to occur during printing with a presensitized plate having an image recording layer containing an infrared absorbent such as a so-called thermal positive type image recording layer in which an infrared absorbent existent in a photosensitive layer manifests its photothermal conversion action and an exposure generates heat, whereby an exposed area in the photosensitive layer becomes alkali-soluble to form a positive image, and a so-called thermal negative type image recording layer in which its exposure-caused heat allows a radical generator or an acid generator to generate a radical or an acid, by which a radical polymerization reaction or an acid crosslinking reaction is accelerated and an image recording layer becomes insoluble to form a negative type image. Taken up as one of the reasons why scum is generated is that since infrared absorbents used in these image recording layers are compounds having a relative higher molecular weight, they are hardly dissolved in a developer and are likely to be adsorbed to the surface of non-image areas on a lithographic printing plate at the time of development.
Conventionally with a presensitized plate having an image recording layer containing the infrared absorbent like this, it is particularly difficult to materialize the production of a presensitized plate excellent in both the above scum resistance and press life.
Accordingly, an object of the present invention is to provide a presensitized plate in particular a presensitized plate which has an image recording layer containing an infrared absorbent and which is excellent in both scum resistance and press life when processed into a lithographic printing plate, a support for a lithographic printing plate for use in the presensitized plate, and a method of preparing the support.
The inventors have found that by using a support for a lithographic printing plate obtained by treating with an aqueous solution containing a divalent or multivalent cation at a low concentration preferably after a hydrophilic treatment is performed, the lithographic printing plate obtained therefrom is excellent in both scum resistance and press life. The present invention has been completed on the basis of the finding described above.
In other words, the present invention provides the following (1) to (10):
(1) A support for a lithographic printing plate obtainable by performing a treatment with an aqueous solution containing one or more divalent or multivalent cations at a concentration ranging from 0.0001 mol/L to less than 0.020 mol/L.
(2) The support for a lithographic printing plate according to (1) above, wherein the treatment with the aqueous solution is performed on an aluminum plate which has been subjected to a graining treatment, an anodizing treatment and a hydrophilic treatment in this order. To be more specific, the support for a lithographic printing plate, wherein the treatment with the aqueous solution containing one or more divalent or multivalent cations at a concentration ranging from 0.0001 mol/L to less than 0.020 mol/L is performed on an aluminum plate which has been subjected to a graining treatment, an anodizing treatment and a hydrophilic treatment in this order.
(3) The support for a lithographic printing plate according to (2) above, wherein the hydrophilic treatment is a treatment with an aqueous solution of an alkali metal silicate.
(4) A method of preparing a support for a lithographic printing plate comprising the step of:
performing a treatment with an aqueous solution containing one or more divalent or multivalent cations at a concentration ranging from 0.0001 mol/L to less than 0.020 mol/L.
(5) The method of preparing a support for a lithographic printing plate according to (4) above, wherein the treatment with the aqueous solution is performed on an aluminum plate which has been subjected to a graining treatment, an anodizing treatment and a hydrophilic treatment in this order.
To be more specific, the method of preparing a support for a lithographic printing plate, wherein the treatment with the aqueous solution containing one or more divalent or multivalent cations at a concentration ranging from 0.0001 mol/L to less than 0.020 mol/L is performed on an aluminum plate which has been subjected to a graining treatment, an anodizing treatment and a hydrophilic treatment in this order.
(6) The method of preparing a support for a lithographic printing plate according to (5) above, wherein the hydrophilic treatment is a treatment with an aqueous solution of an alkali metal silicate.
(7) A presensitized plate which comprises a support for a lithographic printing plate according to any one of (1) to (3) above and an image recording layer formed thereon.
(8) The presensitized plate according to (7) above, wherein the image recording layer is an image recording layer containing an infrared absorbent.
(9) The presensitized plate according to (7) or (8) above, wherein an intermediate layer containing a high-molecular compound having a constituent with an acid group and a constitutent with onium group is formed between the support for a lithographic printing plate and the image recording layer.
(10) A method of preparing a lithographic printing plate comprising the steps of:
exposing a presensitized plate according to any one of (7) to (9) to light; and
developing the exposed presensitized plate using a developer substantially containing no alkali metal silicate to thereby obtain the lithographic printing plate.